Glasses doped with rare-earth ions are proving to be luminescence materials as they have high emission efficiencies. These emissions correspond to 4f–4f and 4f–5d electronic transitions. The 4f–4f transition gives an especially sharp fluorescence pattern from the ultraviolet to the infrared region. Then it has been widely studied and applied in a variety of photonic applications, e.g., solid-state lasers, waveguide lasers, optical fibers and optical amplifiers.
Er3+ ion is one of the most studied rare-earth ions as well as one of the most efficient ions for photonic devices .